Magnetic pressure indicator



Feb. 19, 1963 Original Filed June 1'?, 1958 ya a D. B. PALJ.v

MAGNETIC PRESSURE INDICATOR 2 Sheets-Sheet l INVENTOR. DAVID B. PALL.

Feb. 19, 1963 D, B. PALL l 3,077,854

MAGNETIC PRESSURE INDICATOR original Filed June 17, 1958 2 sheets-sheet2 'l nited rates listens Sar 3,677,854 MAGNETIC PRESSURE iNDliQATUlRDravid B. Pall, Roslyn Heights, Nfir'., assigner to lal gorporatiou,Glen Cove, NX., a corporation ot' New Orlr @riginal application June 17,i953, Ser, No. 742,657, new Patent No. 2,942,572, dated .lune 2t?, 1960.Divided and this application Fel. 29, 1h60, Ser. No. 11,928

6 Claims. (Cl. 116-70) This invention relates to pressure indicatingdevices and, more particularly, to a new and improved magnetic devicefor indicating the occurrence of pressure differences greater than apredetermined value.

In hydraulic systems wherein tluid such as oil or the like is passedthrough a filter, it is desirable to provide external means forindicating clogging of the filter element such as by accumulation ofsufficient dirt to impede the `flow `of fluid. inasmuch as the pressuredrop across the filter increases in proportion to the accumulation ofdirt in the filter element, a suitable indicaiton may be obtained byutilizing a differential pressure device set to be actuated when thepressure drop in the filter reaches a predetermined value. At lowtemperatures, however, the increased viscosity of many iiuids such asoil results 4in increased pressure dre-p across the iilter even thoughthe filter element may not be clogged.

Accordingly, it is an object of this invention to provide a new andimproved pressure indicator utilizing mag* netic attraction settable torespond when a predetermined pressure is obtained.

Another object of the invention is to provide a pressure indicator ofthe above character adapted to detect clogging of the filter element.

A further object of the invention is to provid-e a pressure indicator ofthe above type which does not respond to increases in pressure resultingfrom low temperature.

These and other objects of the invention are accomplished by utilizing afirst magnetic element arranged to attract a second magnetic element aslong as the two elements are separated by less than a predetermineddistance. In one embodiment of the invention, the lirst magnetic elementis movable with a piston responsive to changes in pressure and isnormally biased toward the second magnetic element by a predeterminedtorce. The second magnetic element, normally retained toward the firstelement by magnetic attraction, is urged away from the first element bya spring capable of overcoming the magnetic attraction when the twoelements are separated by the predetermined distance. ln order toprevent actuation at low temperatures, a lvl-metallic strip ispositioned to prevent motion of the second magnetic element when thetemperature is below a predetermined value.

Further objects and advantages of the invention will be apparent from areading of the following description in conjunction with theaccompanying drawings in which:

HG. l is a view partially in longitudinal section taken through atypical pressure indicator arranged according to the invention.

FIG. 2 is a sectional view taken on the lines Z-Z of NG. l and lookingin the direction of the arrows.

As shown in FIG. l, a representative pressure indicator arrangedaccording to the invention comprises two magnetic elements 1@ and ilcoaxially mounted on opposite sides of a separating wall 12 within ahousing t3. Preferably, both the elements ld and lll are composed oipermanently magnetized Alnico V or the like and are positioned withopposite magnetic poles adjacent the wall l2 so that each is drawntoward the wall by the resulting force of attraction.

Mounted in a tubular piston it, the magnet le -is slidably supported ina cylindrical bore l in the housing i3l and is urged toward the wall l2by a coil spring lle. in order to prevent liuid from passing from oneend of the bore 15 to the other, a liquid-tight seal is provided bctweenthe bore and the piston l-l by a ring lea of Teflon or other suitablematerial. The coil spring le is selected according to the desiredactuating pressure to permit the piston 1d to move downwardly in thebore l5 when the pressure at the upper end of the piston M exceeds thatat the lower end by an amount equal to .the actuating pressure.

In the illustrated embodiment of the invention, the pressure indicatoris arranged to measure the pressure drop across a filter. Thus, fluidunder pressure is applied to the filter from an inlet line and emergesthrough an outlet line, the difference in pressure between the inlet andoutlet lines being a measure of the resistance and, therefore, theclogging ot the filter l?. in order to detect this pressure difference,a duct Ztl leads from the inlet line 1S to the end of the cylindricalbore l5 adjacent the wall 12 while the other end of the borecommunicates with the outlet line 19.

If desired, in order to prevent dirt carried by the incoming iiuid fromreaching the bore l5 and to make certain that any fluid which might passthrough the bore to the `outlet line is clean, a suitable filter element21 may be inserted in an enlarged portion 22 of the duct Ztl. As shownin FIG. l, the enlarged portion 22 may, for example, be a ring-shapedcavity in the housing 13 surrounding one of the magnetic elements.Within this cavity, an annular lter element 2l is inserted, therebyproviding a high dirt capacity with low resistance to fluid i'low. Forease in assembly and replacement of the filter element 2l, the housing13 may be separable through the enlarged area 22 into two portions 23and 24 which are joined as by screw threads 25, suitable glands 26 beingprovided to seal the enlarged area of the duct.

On the other side of the wall l2, the magnetic element 11 is slidablyreceived at one end. in a bore 27 coaxial with the bore l5. Secured tothe opposite end of the magnet 1l by a press fit, for example, a cap 28includes a tubular wall 29 extending toward the housing i3 and radiallyspaced from the magnet. The annular' recess 3d thus formed receives acoil spring 3l which extends from the cap 2S to the housing i3 to urgethe cap and the magnet 1l away from the wall l2. This spring is selectedso that it is retained in the stressed condition with the magnet llagainst the wall l2 by the attractive force of the two magnetic elementsas long as the adjacent poles of the two magnets are separated by lessthan a predetermined distance, or example, one-sixteenth of an inch.Whenever the magnetic element liti is moved away from the element lil sothat their adjacent poles are separated by more than a sixteenth of aninch, however, the decreased force of magnetic attraction resultingtherefrom is overcome by the force of the spring .""sil and the cap 2Sand element ll are driven away from the wall l2.

in order to prevent the magnet il from being driven completely out ofthe bore 27, the tubular wall Z@ terminates in a radial iiange 32, and adrum 35, having a central aperture slightly smaller than the flange 32but large enough to permit the cap 28 to pass through it, is mounted onthe housing i3. Also, a conventional bimetallic element is mounted atone end on the inside surface orc the drum 33 as by a weld 3e. As bestseen in FIG. 2, the bimetallic element is preferably comprised of twoarcuate strip portions 3? and joined 'oy a weld 39 and both arranged tobend inwardly with decreasing teinperatures. At normal temperatures, theelement which is adjacent the wall 2Q and just above the flange 32 whenthe indicator is not actuated, has a minimum radius greater than thator" the flange 32 and permits the cap Za'i to rise through the aperture3d on actuation. Howser ymounted in the sleeve a lever 4i is pivotailysupported with one arm 4i?. extending above the cap Positioned above thcarm d?, a switch actuator' is movable by the arm to actuate the switchSil when the cap 23 rises out of the drum 3.. In order to restrictmotion of the magnet lll, an adjustable set screw is mounted in thesleeve to intercept the other arm 415 of the lever di. If desired, thisscrew may be set to stop the lever di after actuation to hold the magnet1l within onesixteenth inch of the normal position of the magnet le,thereby making the indicator automatically resettable in the mannerdescribed above, if the lever motion is not so restricted, the indicatormay be reset by manual rotation of the lever di. To provide a remoteindication of actuation of the indicator, suitable conductors fi-da fromthe switch itl are arranged in any conventional manner to completeappropriate electrical circuits whenever the switch is operated orreset.

in operation, lluid under pressure from the inlet line passes throughthe duct 2id and the filter 2l to the top of the cylindrical bore l5,urging the magnet tti and the piston Kili downwardly against the forceof the spring lo and the pressure from the outlet line. Whenever thedifference between the inlet and outlet pressures is greater the forceof the spring lo, the piston ifi is driven downwardly in the bore l'.After the magnet lo has moved to a position more than one-sixteenth ofan inch away from the magnet il., the attractive force between the twomagnets is less than the force ot the spring 3l and the magnet elementil is driven away from the wall l2 until the ilange 32 abuts the insidesurface of the drum 33. rhus, the cap rises whenever the pressuredifference is greater than the predetermined value in accordance withwhich the spring lo has been selected. As an example, the spring lo maybe arranged to permit the magnet .lo to be driven away from the wall 12when the pressure difierence exceeds 35 psi. and return when thepressure is less than psi. Driven by the spring 3i, the magnet El risesthrough the aperture 34 trrning the lever di to actuate the switch Si).if the set screw #ifi is appropriately adjusted to restrict the motionof the maget il, return of the magnet to its normal position draws themagnet El bach toward the wall EZ, restoring the switch.

it will be apparent that by suitable dimensioniug of the drum 33 and theradial flange 32, the magnet il may be permitted to move more thanone-sixteenth inch from the normal position of the magnet it?. ln thiscase, the pressure indicator must be reset my manual depression ot' thecap On the other hand, if t.e flange 32 is positioned to stop the magnetlill less than one-sixteenth inch `from the normal position oi themagnet lil, the indicator will be automatically reset by the attractiveforce ci the magnets, which is greater than that ot the spring Si. atthis distance, when the magnet l@ is returned to the wail l2.

At temperatures below 32 F., for example, the ther- --ostatic eleme t 35contracts to move the inner end or the strip 3@ over the ilange Thus,when the piston id and the magnet are moved away from the wail l2pressure resulting from increased viscosity of the fluid, e lower edgeof the strip 33 intercepts the fiange 32 preventing a false indicationof liiter clogg'ug.

operation, pressure sufllcicnt to overcome the force of the spring.rives the magnet away from the wall l2 releasing the magnet it.

Although the invention has been describe herein the reference tospecific embodiments, many modifications and variations therein willreadily occur to those skilled in the art. Accordingly, all suchvariations and modifications are included within the intended scope ofthe invention as defined by the following claims.

rhis application is a division or Serial No. 742,657, flled June i7,1958, now US. Patent No. 2,942,572.

l claim:

l. A p essuie indicating device comprising a housing, piston meansmovably mounted in the housing, first magnetic means movable with thepiston means toward and away from a first position, -bias means urgingthe piston cans in one direction and normally retaining the firstmagnetic means in the first position, fluid duct means communicatingwith a source of fluid under pressure and with one end of the pistonmeans to urge it in the opposite direction, second magnetic meansmovable toward and away from the first magnetic means and normallyretained toward the first magnetic means by magnetic attraction when thenrst magnetic means is in the first position, spring bias means urgingthe second magnetic means away from l the first magnetic means selectedto overcome the force of magnetic attraction when the first magneticmeans is more than a predetermined distance away from the secondmagnetic means, and switch means operable by motion of the secondmagnetic means away from the first magnetic means.

2. A pressure indicator according to claim l including stop meansadjustable to prevent the second magnetic means from moving more thanthe predetermined distance from the first position of the first magneticmeans.

3. A pressure indicator according to claim 2 including thermostat meansoperable to prevent the second magetic means from moving away from thefirst magnetic means when the temperature is below a predeterminedvalue.

4. A. pressure indicator according to claim 3 including llange means onthe second magnetic means and wherein the thermostat means comprises abimetallic strip adapted to bend toward the second magnetic means withdecreasing temperature to engage the flange means.

5. A pressure indicating device comprising a housing, piston meansmovably mounted in the housing, first magnetic means movable with thepiston toward and away from a rst position, spring ias means urging thepiston means in one direction and normally retaining the rst magneticmeans in the first position, first fluid duct means communicating with afirst source of iluid under pressure and with one end of the pistonmeans t0 urge it in the opposite direction, second fluid duct meanscommunicating with a second source ot fluid under pressure and with theother end of the piston means, second magnetic means movable toward andaway from the first magnetic means and normally retained toward thefirst magnetic means by magnetic attraction when the first magneticmeans is in the Erst position, spring bias means urving the secondmagnetic means away from the first magnetic means selected to overcomethe force o magnetic attraction when the first magnetic means is morethan a predetermined distance away from the second magnetic means, andswitch means operable by motion of the second magnetic means away fromthe first magnetic means.

6. A pressure indicating device comprising a housing, piston meansmovably mounted in the housing, first magnetic means movable with thepiston toward and away from a first position, spring bias means urgingthe piston means in one direction and normally retaining the firstmagnetic means in the first position, first lluid duct meanscommunicating with a first source of fluid under pressure and with oneend or the piston means to urge it in the opposite direction, secondfluid duct means communicating with a second source of fluid underpressure and with tbe other end or the piston means, filter means in theiirst luid duct means for preventing impurities in the first source fromreaching the piston means or the second motion of the second magneticmeans away from the first source, second magnetic means movable towardand away magnetic means.

from the rst magnetic means and normally retained toward the firstmagnetic means by magnetic attraction References Cited m the flle 0f hlSPiltent when the rst magnetic means is in the first position, 5 UNITEDSTATES PATENTS spring bias means urging the second magnetic means away2,669 707 Ehrman F611 16 1954, from the first magnetic means selected toovercome the 759:061 Ede1man Aug 14, 1956 force of magnetic attractionwhen the irst magnetic means 2,803,718 Bloom Aug. 20, 1957 is more thana predetermined distance away from the 2,843,077 Leefer July 15, 1958second magnetic means, and switch means operable by lo 2,942,572 PallJune 28, 1960

1. A PRESSURE INDICATING DEVICE COMPRISING A HOUSING, PISTON MEANSMOVABLY MOUNTED IN THE HOUSING, FIRST MAGNETIC MEANS MOVABLE WITH THEPISTON MEANS TOWARD AND AWAY FROM A FIRST POSITION, BIAS MEANS URGINGTHE PISTON MEANS IN ONE DIRECTION AND NORMALLY RETAINING THE FIRSTMAGNETIC MEANS IN THE FIRST POSITION, FLUID DUCT MEANS COMMUNICATINGWITH A SOURCE OF FLUID UNDER PRESSURE AND WITH ONE END OF THE PISTONMEANS TO URGE IT IN THE OPPOSITE DIRECTION, SECOND MAGNETIC MEANSMOVABLE TOWARD AND AWAY FROM THE FIRST MAGNETIC MEANS AND NORMALLYRETAINED TOWARD THE FIRST MAGNETIC MEANS BY MAGNETIC ATTRACTION WHEN THEFIRST MAGNETIC MEANS IS IN THE FIRST POSITION, SPRING BIAS MEANS URGINGTHE SECOND MAGNETIC MEANS AWAY FROM THE FIRST MAGNETIC MEANS SELECTED TOOVERCOME THE FORCE OF MAGNETIC ATTRACTION WHEN THE FIRST MAGNETIC MEANSIS MORE THAN A PREDETERMINED DISTANCE AWAY FROM THE SECOND MAGNETICMEANS, AND SWITCH MEANS OPERABLE BY MOTION OF THE SECOND MAGNETIC MEANSAWAY FROM THE FIRST MAGNETIC MEANS.